This invention relates to an apparatus and method for enhancing heat transfer in a heat exchanger.
Heat exchangers typically involve a fluid flowing in a conduit and the exchange of heat between the fluid and the conduit. For example, chemical process plants typically use shell and tube-type heat exchangers to provide heat exchange between a fluid and a conduit.
In the design of heat exchangers, it is well known that heat transfer between a fluid flowing along a heat exchanger surface or conduit is confined primarily to a layer of fluid in contact with the heat exchanger surface. Previous attempts to enhance heat transfer include fin structures extending from the heat exchanger surface and contacting the fluid to set up a flow disturbance which prevents the stratifying or laminar flow of the fluid flowing against the heat exchanger surface. The fins typically are formed to contact the heat exchanger surface and provide higher conductive heat transfer from the fluid to the surface.
An insert device known as a turbulator has been employed in heat exchangers to provide a turbulent flow of the fluid against the inside surface of the conduit or tube in which the fluid is flowing. The turbulator in the tube improves heat transfer primarily by slowing down the velocity of the fluid flowing through the central portion of the tube or pipe cross section, and further improves the temperature distribution of the fluid in the cross section of the tube or conduit by conduction and mixing.
It is known that heat transfer applications at high temperatures involve a radiation of heat transfer which takes on a dominant influence over convection and conductive heat transfer. Attempts have been made to take advantage of higher radiation heat transfer by providing reradiant inserts. An example of a reradiant insert would be a gas recuperator as is disclosed in Kardas et al U.S. Pat. No. 3,886,976. The Kardas insert uses a floating extended surface which provides an additional area for accepting heat by convection and radiation from the hot gas in the recuperator, the Kardas insert not being integrally connected with the original heat receiving surface. Heat is retransmitted to the intended heat transfer surface by a continuous spectrum of Stefan-Boltzmann radiation. The Kardas et al patent discloses that radial mixing and large effecting radiating area can be obtained by using multileaf reradiators of the type shown in the Kardas patent in FIG. 5.
However, the aforementioned fins, turbulators, and recuperators have a major drawback in that these devices require a significant pressure drop through the conduit. Further, the aforementioned turbulators and fins are designed for lower temperature operation and do not produce the most efficient heat exchange insert at higher temperatures.
It is an object of the present invention to provide heat exchanger apparatus and method for enhancing heat exchange between a fluid and a heat exchanger surface such as a heat exchanger tube or conduit.
It is another object of the present invention to provide heat exchanger apparatus and method of enhanced efficiency at higher temperature differences between the fluid and heat exchanger surface.
It is yet another object of the present invention to provide heat exchanger apparatus and method of enhanced efficiency requiring a minimum pressure drop through the heat exchanger.